1. Field of the Invention
The invention relates to a circuit board, a manufacturing method thereof, and an electro-optic apparatus, and more particularly, to a circuit board connecting to an electro-optic device, a manufacturing method thereof, and an electro-optic apparatus having the circuit board.
2. Description of Related Art
With the increase in information capacity, in addition to communication fields such as trunk lines and access systems, the information processing in routers and servers are also currently using light interconnection techniques. In particular, circuit boards having optical transmission paths are developed to transmit light for the short-range signals between or inside the boards of routers and servers. In terms of the optical transmission path, waveguides have higher degrees of freedom than optical fibers in wiring, and waveguides may be densely packed.
In general, the manufacturing method of a circuit board having an optical transmission path includes first forming a waveguide layer on the substrate having a circuit pattern. Then, forming the needed dielectric layers and other circuit patterns on the substrate by the build-up technique. Then, forming openings exposing the sidewalls of the waveguide layer in the dielectric layer on the substrate to form the light entrance and the light exit on the two ends of the waveguide layer. When the electro-optic device is connected to the circuit board, optical signals may enter the waveguide layer through the light entrance and exit the waveguide layer through the light exit.
In the current manufacturing method, laser cutting or mechanical drilling is usually used to form the opening. However, when forming an opening with laser cutting or mechanical drilling, the sidewalls of the waveguide layer usually have significant surface roughness. In this way, when the optical signal enters the waveguide layer through the light entrance and exits the waveguide layer through the light exit, the optical signal is significantly depleted, affecting the performance of the apparatus.